Hundreds of people have been arrested on terrorism-related charges across the United Kingdom this year, foiling several potentially deadly attacks, the Scotland Yard said, according to media reports. In a statement, Assistant Commissioner Mark Rowley, Scotland Yard’s head of counterterrorism, reportedly said that 218 people have so far been arrested this year in terror-related cases.

The police “are running exceptionally high numbers of counter-terrorism investigations, the likes of which we have not seen for several years,” Rowley reportedly said. “We are disrupting several attack plots a year. These plots are of varied sophistication, from individuals planning to carry out spontaneous yet deadly attacks to more complex conspiracies, almost all seemingly either directed by or inspired by terrorism overseas.”

Rowley’s statements come at a time when authorities in the U.K. are on high alert following Prime Minister David Cameron’s pronouncement in September that the Islamic State group posed the country’s “greatest-ever security risk.” In August, Britain had raised its terror threat level to the second-highest classification of “severe,” suggesting that an attack on the U.K. was “highly likely.”

Last week, Scotland Yard, in a joint-operation with MI5, U.K.’s counterintelligence and security agency, had arrested four people planning a “significant” attack in the country.

Rowley also said that the police are being “stretched” by the “volume, range and pace of counterterrorism activity” needed to counter the increasing radicalization of young British nationals.

“Extremist groups are using social media in highly sophisticated ways in order to recruit or persuade individuals towards their violent and warped ideologies,” he reportedly said, adding that a specialized unit has been set up to ensure “de-radicalization” of the “young, impressionable, and in some cases vulnerable individuals.”

According to a report by The Guardian, about 50 people are being referred to de-radicalization programs in the U.K. every week, including a large number of people arrested in “Syria-related preventive activities.”

“This is a terrorist threat that may have its seat somewhere that seems a long way away but it is influencing people on the streets of London and is trying to import terrorism onto the streets of London and the U.K.,” Rowley reportedly said.